Time calculations for Word 2007 schedule

I know I've done this before, I just can't remember how. I have a schedule that needs to be printed monthly, based on sunset. So i have a table with 4 or 5 columns. I want to enter one value in each column (x) and have the rest of the value calculated automatically.
The calculations I need are as follows:
(x - 1 hour) rounded to the nearest 5 minutes
(x - 70 minutes)
(x - 40 minutes)
This doesn't seem to be so difficult - I just don't remember how to do it!
TIA

While this kind of thing can be done with Word without macros (see http://windowssecrets.com/forums/sho...ation-Tutorial) or with macros, the process is far more complex than it would be if you used Excel. Excel can do the lot automatically with fairly simple formulae and no macros. It is therefore a much more appropriate tool for the job than Word will ever be.